Borated friction reducing additives and compositions thereof

1. Field of the Invention

This invention relates to lubricant additives and compositions thereof and more particularly to compositions comprising a major proportion of an oil of lubricating viscosity or a grease prepared therefrom containing a minor effective amount of a multifunctional additive consisting of borate esters of hydrolyzed hydrocarbyl alkoxides. Further, this invention relates to the described additives incorporated into lube oils in effective friction-reducing amounts.

2. Description of the Prior Art

It is well known that lubricants by definition reduce friction between moving surfaces; however, friction-reducing additives are agents which, when added to lubricants in minor amounts, significantly enhance the frictional or lubricity properties of those lubricants without modifying their other physical properties such as viscosity, density, pour point and the like.

Alcohols, for example, have long been known for their lubricity properties when formulated into lubricating oils and for their water scavenging characteristics when incorporated into fuel formulations. Hydrocarbon soluble epoxidized fatty acid esters prepared by the epoxidation of unsaturated carboxylic acid esters are also known to have been used as anti-wear and anti-friction additives in lubricants as described in U.S. Pat. No. 4,244,829. Borated hydrolysis products of 1-(2-hydroxyalkyl)-2-alkyl or alkenylimidazolines are known to be effective friction modifying additives as described in U.S. Pat. No. 4,273,665. Further, the use of vicinal hydroxyl containing alkyl carboxylates such as glycerol monooleate have also found widespread use as lubricity additives.

U.S. Pat. No. 4,410,438 to Horodysky discloses borated epoxide additives and lubricants prepared therefrom. In preparation of the additives, an epoxide is reacted with boric acid, boron oxide or an alkyl borate in the absence of added water.

It has now been found that borate esters of hydrolyzed hydrocarbyl alkoxides can significantly reduce friction of lubricants and add a new dimension of anti-oxidation and high temperature properties to lubricant compositions. The borate esters described herein also possess improved solubility characteristics over those of non-borated derivatives, especially in synthetic fuels. Additionally, these novel additives are non-corrosive to copper and possess anti-wear properties and the ability to provide anti-fatigue characteristics to lubricants or greases containing same.

The additive compounds useful in this invention are long-chain hydrocarbyl terminal epoxides which have been hydrolyzed using boric acid catalysis and borated to form a mixture of borate esters of the corresponding diols and borate esters of oligomers of the alkyl epoxides which polymerize during hydrolysis. The additive compounds formed in this way are very different from, and often superior to, borate esters, formed by boration of the corresponding preformed diols made by traditional hydrolysis of the described long-chain alkyl epoxides. This invention also includes a novel process to make these boronated esters via boric acid catalysis and boronation to form the disclosed mixture of esters of the diols along with borate esters of oligomers of the epoxides which polymerize during boric acid catalysis. The alkyl groups of the long-chain alkyl epoxides contain at least 14 carbon atoms and up to 36 or more carbon atoms. The epoxide group can be anywhere along the chain, but preferably in the 1,2 or terminal position. The hydrocarbyl epoxides can be straight chain, or branched chain or contain cyclic groups or unsaturated groups, but is preferably saturated alkyl. Preferred epoxides include 1,2-epoxynonadecane, 1,2 -epoxyheptadecane, 1,2-epoxytetradecane, 1,3-epoxyhexadecane, 1,2-epoxypentadecane, 1,2-epoxyoctadecane and the like, and mixtures of similar epoxides.

Lubricant compositions comprising oils of lubricating viscosity and greases prepared therefrom containing these novel additives possess multi-functional characteristics. Further, when moving surfaces of, for example, internal combustion engines, are treated with lubricant compositions containing these novel additives, a means or method of obtaining improved fuel economy for said engines is provided.

The amount of additive in the lubricant compositions may range from 0.1 to about 10% by weight of the total lubricant composition. Preferred is from about 0.5 to about 5 wt. %.

The novel compositions embodied herein can, and usually do, include other materials such as corrosion inhibitors, viscosity index improvers, extreme pressure agents, detergents, dispersants, antiwear additives, all of which impart their customary properties to the particular compositions and do not detract from the value of the compositions into which they are incorporated. Such additives often include succinimides, sulfonates, phenates, olefin copolymers, methacylates, zinc dithiophosphates, overbased calcium or magnesium salts and the like. In fact, the disclosed friction reducers often are preferably used with zinc dithiophosphates and in such formulations exhibit significant activity. That is, the novel additives disclosed herein do not prevent these other additives from performing their known purposes, nor are they prevented from performing their purpose by the presence of such other additives. Generally, the total amount of all such materials will not exceed about 10 to 20 wt. %.

The product should contain at least 0.1% boron and may contain 10% or more boron. At least a 5-10% portion of available epoxide groups should preferably be borated. Also, a stoichiometric excess of boronating agent can effectively be used.

The lubricants contemplated for use herein include both mineral and synthetic hydrocarbon oils of lubricating viscosity, mixtures of mineral and synthetic oils, and greases prepared therefrom, and other solid lubricants. The synthetic oils may include polyisobutylenes, hydrogenated olefins, polypropylene glycol, di(2-ethylhexyl) sebacate, dibutyl phthalate, neopentyl esters, pentaerythritol esters, trimethylol propane esters, fluorocarbons, silicate esters, silanes, hydrogenated mineral oils, chain-type polyphenyl, siloxanes and silicaones, and phenoxy phenylethers. Preferred are synthetic formulations. Where the lubricant is to be employed in the form of a grease, the lubricating oil is generally employed in an amount sufficient to balance the total grease composition, after accounting for the desired quantity of the thickening agent and other additive components to be included in the grease formulation. A wide variety of material may be employed as thickening or gelling agents. These may include any of the conventional metal salts or soaps, such as lithium or calcium which are dispersed in the lubricating vehicle in grease-forming quantities in such degree as to impart to the resulting grease composition the desired consistency. Included are lithium or calcium 12-hydroxystearates or stearate soaps or similar metal soaps or non-soap thickeners, such as surface-modified clays and silicas, aryl ureas, calcium complexes and similar materials. In general, grease thickneners may be employed which do not melt and dissolve when used at the required temperature within a particular environment; however, in all other respects, any materials which are normally employed for thickening or gelling hydrocarbon fluids for forming grease can be used in preparing the aforementioned improved grease in accordance with the present invention.

The compounds of this invention may, inter alia, be prepared by reaction of the aforementioned alkoxides with water in the presence of a suitable catalyst, thereafter borated in the presence of a boron-containing reactant and catalyst. The use of more traditional catalysis such as sulfuric acid, hydrochloric acid or p-toluene, sulfonic acid catalysis during this reaction step does not form the same product as is formed by the co-reaction of long-chain epoxide and water and boronating agent. The compounds of this invention are uniquely formed in a one-pot, one-step combined boronation, hydrolysis, polymerization reaction involving the hydrocarbyl epoxides starting materials. No prior art known to applicants describes such compositions, lubricant compositions thereof or the unique process of making such materials. It is not necessary to use the preferred boric acid. Boronating agents such as low-molecular weight trialkyl borates which will form boric acid in the presence of water can also be used. For convenience, however, the boration and hydrolysis may be carried out in a single pot using substantially stoichometric amounts of water. The reaction can be is also carried out in the presence of a solvent having a low boiling temperature such as ethanol or butanol, or other solvent such as toluene or xylene. The reaction time can vary from 2 to about 14 hours. The preferred reaction time is from 4 to about 12 hours. The reaction temperature can vary from about 150° C. to 250° C.

The invention having been described in general terms, the following specific illustrations thereof are offered; however, it is to be understood that they are illustrated only and that the invention is not thereby limited except as by the appended claims.

Low Velocity Friction Apparatus (LVFA)

The Low Velocity Friction Apparatus (LVFA) is used to measure the friction of test lubricants under various loads, temperatures, and sliding speeds. The LVFA consists of a flat SAE 1020 steel surface (diam. 1.5 in.) which is attached to a drive shaft and rotated over a stationary, raised narrow ringed SAE 1020 steen surface (area 0.08 in 2 ). Both surfaces are submerged in the test lubricant. Friction between the steel surfaces is measured as a function of the sliding spped at a lubricant temperature of 250° F. The friction between the rubbing surfaces is measured using a torque arm strain guage system. The strain guage output, which is calibrated to be equal to the coefficient of friction, is fed to the Y axis of an X-Y plotter. The speed signal from the tachometer-generator is fed to the X-axis. To minimize external friction, the piston is supported by an air bearing. The normal force loading the rubbing surfaces is regulated by air pressure of the bottom of the piston. The drive system consists of an infinitely variable-speed hydraulic transmission driven by a 11/2 HP electric motor. To vary the sliding speed, the output speed of the transmission is regulated by a lever-cam-motor arrangement.

Procedure

The rubbing surfaces and 12-13 ml of test lubricant are placed on the LVFA. A 500 psi load is applied, and the sliding speed is maintained at 30 fpm at ambient temperature for a few minutes. A plot of coefficients of friction (U k ) over a range of sliding speeds, 5 to 40 fpm (25-195 rpm), is obtained. A minimum of three measurements is obtained for each test lubricant. Then, the test lubricant and specimens are heated to 250° F., another set of measurements is obtained, and the system is run for 50 minutes at 250° F., 500 psi, and 40 fpm sliding speed. Freshly polished steel specimens are used for each run. The surface of the steel is parallel ground to 4 to 8 microinches. The percentages by weight are percentages by weight of the total lubricating oil composition, including the usual additive package. The date are percent decrease in friction according to: ##EQU1##

Thus, the value for the oil alone would be zero for the form of the data used in the Table below.

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Friction Test Results Using

Low Velocity Friction Apparatus

Additive

%

Conc. in

Reduction in Coefficient

Base of Friction in LVFA at

Blend 5 Ft./Min.

30 Ft./Min.

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Base Blend (fully formulated

-- 0 0

SAE SW/30 synthetic

engine oil containing

detergent/dispersant/

inhibitor package)

Base Oil (200

-- 67 3.62 -1.2

second solvent

paraffinic neutral

lubricating oil)

Borated, hydrolyzed,

1 17 2.08 0.0

1,2-epoxy

mixed C.sub.15 -C.sub.18 alkanes

0.5 19 2.03 0.0

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The results disclosed by the data in Table 2 clearly show the stability exhibited by these multi-purpose friction reducers in the presence of catalytic metals under severe oxidizing conditions at elevated temperatures.

Example 1 was further subjected to the Copper Strip Corrosivity Test. The test was run in 200 second, solvent paraffinic neutral lubricating oil in accordance with ASTM D-130-80. The results disclosed in Table 3 clearly show the borate esters to be non-corrosive to copper.

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Copper Strip Corrosivity Characteristics

Add-

itive Test Rating

Conc. ASTM D130-80

ASTM D130-80

6 hrs @ 210° F.

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Borated, hydrolyzed,

1 1A 1A

1,2-epoxy

mixed C.sub.15 -C.sub.18 alkanes

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The data disclosed hereinabove dramatically illustrate that borate esters of boron-catalyzed hydrolyzed hydrocarbyl epoxides and compositions containing same can be used to substantially improve the gasoline fuel economy of already fuel efficient synthetic motor oils, and a variety of other lubricants (including both synthetic and mineral oil based automotive and industrial lubricants and greases). Furthermore, these additives have multi-functional characteristics. In addition to friction reducing properties, they also provide anti-corrosion, anti-oxidation, anti-wear and high temperature properties not generally available in a single lubricant additive.

It is understood by those of ordinary skill in the art that variations of this invention within the scope thereof can be readily made.